I. Field
The present disclosure relates generally to communication, and more specifically to techniques for performing fast Fourier transform (FFT) processing and demodulation in a system with multiple subcarriers.
II. Background
Orthogonal frequency division multiplexing (OFDM) is a modulation technique that partitions a frequency band (e.g., the system bandwidth) into multiple (N) orthogonal subcarriers. These subcarriers are also referred to as tones, bins, subbands, and so on. With OFDM, each subcarrier may be independently modulated with data.
OFDM is widely used in various communication systems. For example, an orthogonal frequency division multiple access (OFDMA) system can support multiple users using OFDM. The N subcarriers may be used for data and pilot transmission in various manners, depending on the system design. For example, the OFDMA system may partition the N subcarriers into multiple sets of subcarriers and may allocate each subcarrier set to a different user. Multiple users may then be supported simultaneously via their assigned subcarrier sets.
In many instances, it is only necessary to demodulate a subset of the N total subcarriers in an OFDM-based system. A straightforward method to process a subset of the N total subcarriers is to perform an N-point FFT on time-domain samples to obtain frequency-domain symbols for all N subcarriers. The symbols for the subcarriers of interest are then extracted and processed, and the symbols for all other subcarriers are discarded. This straightforward method requires an N-point FFT for all N subcarriers even if only a small subset of these N subcarriers is of interest.
There is therefore a need in the art for techniques to more efficiently perform FFT processing and demodulation in a system with multiple subcarriers.